Garbage and refuse incinerators, commonly give rise to dust-form substances which are predominantly recovered in the form of fly ash and, as noted, but also can include finely divided coal products, finely divided coke particles and the like. The dust-form particles also include reaction products resulting from the flue gas treatment, e.g. by the addition of reactants seeking to combine sulfur or sulfur containing compounds, metal rich dust, condensate and grate ash or the like. The dust like substances may be separated out prior to treatment of the flue gas, during the cleaning of the flue gas or derived from the processing of ash. As mentioned such dust-form substances containing toxic or noxious materials and thus disposal of them frequently poses a problem or can be comparatively expensive.
It has been proposed heretofore to eliminate such materials or dispose of them by a smelting process. For example, a smelting furnace which is heated by special heating rods has been described in which the heat of the rods is transformed exclusively by reaction to the melt. The melt is a glass slag melt.
The dust-form materials to be disposed of are spread upon the glass slag melt by means of a worm conveyor.
In another approach, a smelting destruction of the dust-form substances from a flue gas cleaning plant is effected with plasma heated burners which may be arranged in a star pattern, at the center point of which, the dust meets the jets of the plasma and is heated.
The molten product drops into the glass slag bath disposed therebelow.
One of the problems of this latter process is that a large proportion of the dust-form substances tends to be entrained from the smelting furnace with the waste gas or smoke flowing therefrom. When the dust-form substances include or are constituted by fly ash, it is found that only about 70% of the fly ash is incorporated into the glass or transformed thereto while the balance is entrained out of the melting furnace.
The high plasma temperature is transferred by both radiation and convection to the dust-form substances and from these substances there can be considerable evaporation losses.
It is also possible, in accordance with prior art techniques to operate with glass melting furnaces in which a glass slag is maintained. In these systems, the dust-like substances to be smelted are spread onto the surface of the glass slag and dispersed thereby by a stirrer.
This arrangement has the drawback that the dispersal of material spread upon the slag may not be sufficiently uniform or is incomplete. The glass melt and the rising gasses are relied upon to heat the floating material to the melting point, and as a consequence, the materials are not fully incorporated into the glass slag. Nonusable residues may also result.
All of these earlier systems are comparatively expensive, are incapable of satisfactorily destroying all of the dust-like substances, are characterized by a high proportion of residues which cannot be processed or are discharged, or give rise to vaporization losses. Accordingly, improvement in the disposal of such dust-like substances is desirable.